Crystal Structure and Physical Properties of a New CuTi₂S₄ Modification in Comparison to the Thiospinel

A new modification of CuTi2S4 was prepared from the elements at 425 °C. It crystallizes in the rhombohedral space group R3̄m, with lattice parameters of a = 7.0242(4) Å, c = 34.834(4) Å, and V = 1488.4(2) Å3 (Z = 12). Two topologically different interlayer regions exist between the close-packed S layers that alternate along the c axis: one comprises both Cu (in tetrahedral voids) and Ti atoms (in octahedral voids), and the second exclusively Ti atoms (again in octahedral voids). In contrast to the known modification, the spinel, Cu−Ti interactions of 2.88 Å occur that have bonding character according to the electronic structure calculations. Both CuTi2S4 modifications are metallic Pauli paramagnets due to Ti d contributions. The Pauli susceptibility of the R3̄m form is larger than that of the thiospinel in quantitative agreement with the LMTO-ASA band structure calculations. The irreversible transformation to the spinel takes place at temperatures above 450 °C.